Method for the removal of NOx and catalyst therefor

ABSTRACT

The invention relates to a method for the catalytic reduction of NO x  in an NO x  containing gas using methane in the presence of a catalyst which comprises a palladium-containing zeolite. In this process one uses a zeolite based on rings of 12 oxygen atoms, wherein the zeolite also comprises scandium, yttrium, a lanthanide or a combination thereof. The invention also relates to the catalyst itself and the preparation thereof.

FIELD OF INVENTION

The invention relates to a method for the catalytic reduction of NO_(x)in an NO_(x) containing gas using methane in the presence of a catalystwhich comprises a palladium-containing zeolite. The invention alsorelates to a catalyst which comprises a palladium-containing zeolite.The invention also relates to the preparation of this catalyst.

BACKGROUND OF INVENTION

NO_(x) is released in combustion processes in, for example, gas engines.At present only very few gas engines are equipped with a deNO_(x)installation. Apart from NO_(x), the exhaust gases of gas enginescontain considerable amounts of uncombusted methane; sometimes up to 3%of the fuel leaves the engine uncombusted. These methane emissions mustalso be controlled as part of the reduction of greenhouse gas emissions.

NO_(x) can also be released from gas burners in horticulture, generatingsets, emergency power supplies, gas turbines of (small-scale) combinedheat and power systems, and in the industrial production of, forexample, cement, nitric aid, iron or caprolactam, in traffic and in theburning of household refuse.

There are various techniques on the market for reducing NO_(x)emmisions, such as low-NO_(x) burners and selective catalytic reductionwith ammonia or urea. These techniques, however, are impossible orexpensive to apply for many (small-scale) (gas burner) installationswhich produce NO_(x). There is therefore a demand for an inexpensivedownstream technique for the reduction of NO_(x).

U.S. Pat. Nos. 5,149,512 and 5,260,043 describe methods in which NO_(x)is removed with the aid of methane and in which inter alia a catalyst isused which consists of a ZSM-5 zeolite loaded with cobalt. Thiscatalyst, however, only has limited activity for the catalytic reductionof NO_(x) with methane. In the absence of water, temperature above 450°C. are necessary for an NO_(x) removal efficiency above 50%. In thepresence of water, however, it must be expected that the NO_(x)conversion will decrease by about half.

According to the review article by Traa et al., Co-ZSM-5 can also beused for the reduction of NO_(x) with propane (Y. Traa, B. Burger, J.Weitkamp, Micr. Mes. Mater. 30 (1999) 3-41). It was found here that themethod of preparation of the catalyst was critical, and that much higheractivities were obtained if the zeolite was loaded with cobalt by theimpregnation method (incipient wetness).

A much more efficient catalyst for the reduction of NO_(x) with methanewas found in the form of ZSM-5 with palladium. It is true that thesezeolites have a higher activity than zeolites based on cobalt, but itturns out that the activity of the Pd zeolite catalyst also decreasesgreatly in the presence of water. Loss of activity is also clearlyobserved as a function of time, (see for example Y. Traa, B. Burger, J.Weitkamp, Micr. Mes, Mater. 30 (1999) 3-41).

Ogura et al. (M. Ogura, S. Kage, M. Hayashi, M. Matsukate and E.Kikuchi, Appl. Catal. B 27 (2000), L213-216) describe the stabilizationof Pd-ZSM-5 with the aid of inter alia cobalt, rhodium, silver, ceriumor iron. It is apparent from his study that cobalt is highly suitable asa stabilizer. Cobalt might also have a promoting effect on the reaction(promotor). The other elements, rhodium, silver, cerium and iron, arepromotors in the reaction and also provide Pd-ZSM-5 stabilization.

From FIG. 3 in this publication, however, it can be deduced thatalthough these elements can have a stabilizing effect (the half-lifeincreases), it also turns out that the initial conversion activitydeceases, if loaded with rhodium the initial activity goes from 49.7% to18.9% (drop of about 60%), with silver the initial activity goes from49.7% to 29.9% (drop of about 40%), with cerium the initial activitygoes from 49.7% to 39.6% (drop of about 20%) and with iron the initialactivity goes from 49.7% to 40% (drop of about 20%). In a number ofcases, this may mean that for a substantial part of its life thestabilized catalyst has a lower activity than the non-stabilizedcatalyst. That is not desirable. The fact that the initial conversionsdiffer so much with the different metal combinations also makes italmost impossible here to check whether there is in fact any stabilizingeffect at all.

Only for the Pd-ZSM-5 catalyst stabilized with cobalt (FIGS. 1 and 2 ofthis publication) does it appear to be true that the activity scarcelydecreases as a result of the addition of (3.3% by weight) cobalt, whilegood stabilization is indeed obtained (in any case for a reaction timeup to about 14 h). On the basis of this article the person skilled inthe art would opt for a Pd—Co-ZSM-5 catalyst for the reduction of NO_(x)using methane. The activity of this catalyst is limited, however: only60% NO_(x) conversion is achieved at 500° C.; the stability after about14 h is not known.

In U.S. Pat. No. 6,063,351 a catalyst based on this palladium-cobaltpairing, with mordenite (MOR) as carrier, is described for the reductionof NO_(x) with methane. This catalyst has markedly improved activitycompared with the cobalt catalyst of the above-mentioned U.S. Pat. No.5,149,512. Experimentally, however, the stability of this catalyst isfound to be inadequate in the long term.

Japanese patent abstracts JP 09 192486, JP 08 164338 and JP 07 32325also describe catalysts in which Pd may be present. However, none ofthese abstracts show or indicate that palladium should be present as anion coordinated by a zeolite. In contrast, for example JP 08 164338describes that Pd (oxide) layers are present on a zeolite, and JP 0732325 describes that oxides are present on a γ-alumina substrate. Thedisadvantages of these catalysts are the same as the disadvantages ofthe other catalysts know from the art and described above.

SUMMARY OF INVENTION

It is therefore the object of this invention to find an efficient methodfor the catalytic reduction of NO_(x) in an NO_(x) containing gas usingmethane, with the aid of a suitable catalyst. It is furthermore anobject of the present invention that this catalytic reduction shall alsotake place efficiently in the presence of water in the NO_(x) comprisinggas. It is also an object to find a catalyst with a high activity forthe catalytic reduction of NO_(x) and with a high stability.

Surprisingly it was found that a zeolite based on rings having 12 oxygenatoms also containing palladium ions, with the zeolite also containingscandium, yttrium, a lanthanide or a combination thereof, givesexcellent results in the catalytic reduction of NO_(x) with the aid ofmethane. In this way an inexpensive NO_(x) reduction technique isobtained. Methane is relatively cheap and available almost everywherefrom the natural gas network. The invention therefore relates to amethod for the catalytic reduction of NO_(x) in an NO_(x) containing gasusing methane in the presence of a catalyst which comprises apalladium-containing zeolite, characterized by using a zeolite based onrings having 12 oxygen atoms, wherein the zeolite also containsscandium, yttrium, a lanthanide or a combination thereof.

The invention also relates to this catalyst which comprises apalladium-containing zeolite, wherein the palladium in the zeolite iswholly or partially coordinated as ion by the zeolite, wherein thezeolite is based on rings of 12 oxygen atoms, and wherein the zeolite isalso loaded with scandium, yttrium or a lanthanide or a combinationthereof.

The invention also relates to a method for the preparation of such acatalyst, wherein the zeolite is loaded with scandium, yttrium, alanthanide or a combination thereof and optionally other metals afterhaving been loaded with palladium by ion exchange.

DESCRIPTION OF INVENTION

In the description of the invention NO_(x) is defined as nitrogen oxideswhere x (or the O/N ratio) is greater than or equal to 1, such as NO,NO₂, N₂O₃ etc. N₂O, laughing gas, is not included in this definition. NOis usually in equilibrium with other nitrogen oxides, where x is greaterthan 1, and oxygen.

“Methane” or a “methane containing gas” means methane, but can also meannatural gas or another gas mixture containing methane and other gases.“Palladium-containing” means that palladium ions are present in thechannels (pores) and/or cages of the zeolite. Lanthanides (Ln) are theelements 57 (La, lanthanum) to 71 (Lu, lutetium) inclusive. “Metal” or“element” means that the elements can be present as a metal, as a metalcompound (notably oxides), but also as an ion of the element/metal.

The NO_(x) containing gas can for example be the gas released by a gasengine or a gas burner, but can also be an exhaust gas from nitric acidsynthesis. The gas can also contain oxygen and/or water. Unlike mostcatalysts according to the prior art, the catalyst according to theinvention loses little or no activity in the presence of water. This istrue in particular if the water is present in quantities up to about5-15%, e.g. 12%, Oxygen can for example be present up to about 20%. Thegas may also contain carbon monoxide (CO), that can be removed(partially or completely) by the catalyst of the invention. Hence, theinvention is also directed to a method where a catalyst is also used forthe removal of NO_(x) and carbon monoxide, e.g., in exhausts of gasengines. CO may be present in amounts of e.g. 1-2000 ppm or more.

The invention encompasses a method for the catalytic reduction of NO_(x)in an NO_(x) containing gas using methane in the presence of a catalystwhich comprises a palladium-containing zeolite, characterized by using azeolite based on rings having 12 oxygen atoms, wherein the zeolite alsocontains scandium, yttrium, a lanthanide or a combination thereof. Theinvention is also direct to such catalyst. The palladium is brought intothe zeolite by ion exchange, before other (active) metals are introducedinto and/or onto the zeolite. The ion exchange step is important, as isalso the order of introduction of the metals. Impregnation is generallya simple and cheaper method of putting metals into a carrier, and thismethod is often used for this reason (among others by Cordoba et al,: L.F. Cordoba, M. Flytzani-Stephanopoulos, C. Montes de Correa, Appl.Catal. B 33 (2001), 25-33).

Cordoba et al. (L. F. Cordoba, M. Flytzani-Stephanopoulos, C. Montes deCorrea, Appl. Catal. B 33 (2001), 25-33) choose a method for thereduction of NO_(x) in which a catalyst is used based oncerium-palladium-mordenite and NO_(x) is reduced with the aid ofdodecane as reducing medium. In this catalyst for this reaction,however, impregnated cerium is the active element and impregnatedpalladium the promotor.

If the catalyst according to Cordoba et al. is used for the reduction ofNO_(x) with methane, this is found to be inadequate: methane ispartially combusted instead of reducing NO_(x). If dodecane has to beused, the presence of PdO (present after impregnation and calcination)is flavourable for the combustion of coke precursors on the catalystsurface. The presence of PdO is found to be unwanted in the case ofmethane, however: methane is oxidized and less reaction with NO_(x) canthen take place. The palladium must therefore be brought into thezeolite by ion exchange, so that the palladium ion (especially as Pd²⁺),wholly or partially coordinated by the zeolite lattice, and not as PdO,is present in the zeolite lattice. For palladium it is surprisinglyfound that it is important for the method of the present invention thatpalladium is introduced by ion exchange. Therefore, the zeolite isloaded with scandium, yttrium, a lanthanide or a combination thereof andoptionally other metals after having been loaded with palladium by ionexchange.

The expression ‘wholly or partially coordinated by the zeolite’ meansthat the palladium has been introduced by ion exchange, and thepalladium as ion (Pd²⁺ for example) is exchanged for cations especiallyin the pores which (via oxygen) are associated with aluminium. Thepalladium ion is therefore exchanged for at least 1 cation of thezeolite and is thus coordinated by the zeolite. The palladium can alsobe coordinated by an anion from the solution (which has been used forthe exchange), but can also be exchanged with a second cation from thepores. In this way the palladium is then completely coordinated by thezeolite and the palladium is in any case after ion exchangesubstantially present as an ion and not as palladium oxide. Palladiummay have been exchanged with H⁺ and NH₄ ⁺, for example. The exchangewill take place particularly in the pores. The zeolite is preferablyloaded with 0.02 to 2% by weight of palladium. Here, “% by weight”refers to the amount of zeolite exchanged with palladium.

The fact that palladium is present as an ion can also be determined withthe aid of IR measurements (FTIR). A non-exchanged zeolite has a latticevibration band at about 1050 cm⁻¹, whereas a zeolite exchanged with Pd²⁺has this band at about 950 cm⁻¹. Such a band at about 950 cm⁻¹ is alsoabsent after impregnation, which means that Pd is not present as Pd-ionsbut as PdO, e.g. as PdO clusters. The catalyst of the present inventiontherefore comprises a zeolite exchanged with Pd²⁺, with an absorptionsignal being found with FTIR at about 950 cm⁻¹, as a result of a zeolitelattice vibration. As described above, this zeolite, based on ringshaving 12 oxygen atoms, has been or is further loaded with scandium,yttrium or a lanthanide or a combination thereof.

The zeolite for the method for the catalytic reduction of NO_(x)according to the invention, in which the palladium is introduced by ionexchange, belongs to the group of zeolites which contain 12-rings (12 Oatoms). The term “12-ring” means that in the zeolite channels or poresare present which are constructed of rings of Si/Al and oxygen and inwhich 12 oxygen atoms are present. Surprisingly these zeolites are foundto be much more satisfactory for the present method than zeolites basedon 10-rings, for example, such as ZSM-5. The zeolite to be usedaccording to the invention therefore comprises a zeolite wherein12-rings are present, such as, for example, FAU, MOR, BRA, EMT, CON, BOGor ITQ-7, etc., or other zeolites based on 12-rings, which are known tothe person skilled in the art, or combinations thereof, e.g. FAU andMOR. The silicon/aluminium ratio is preferably 2 or greater.Particularly good results are achieved when the zeolite is MOR.

Scandium, yttrium and/or one or more lanthanides are put in the zeoliteas a stabilizing element. Examples of these elements are lanthanum,cerium, praseodymium, gadolinium, terbium, dysprosium, or combinationssuch as cerium and gadolinium, etc. Thee introduction can take place byion exchange in the liquid phase, but the loading can also be obtainedby pore volume impregnation (incipient wetness technique). Hence, theinvention also comprises a method where the zeolite is loaded withscandium, yttrium, a lanthanide or a combination thereof by ion exchangeor incipient wetness techniques. It is important that this step takesplace after the introduction of the palladium ion. Surprisingly it isfound that this combination of (a) a Pd zeolite based on rings having 12oxygen atom, where (b) the zeolite also contains scandium, yttrium, alanthanide or a combination thereof, gives excellent results in thepresent method for the catalytic reduction of NO_(x) in an NO_(x)containing gas using methane. The second element increases the stabilityand preferably furthermore increases the initial activity, even in thepresence of water.

In another embodiment, the zeolite is loaded with scandium, yttrium, alanthanide or a combination thereof by physically mixing the zeolitewith salts or oxides of said metals. Also this method to obtain thecatalyst provides good results for the method of the invention for thecatalytic reduction of NO_(x) with methane. Here, the term ‘loaded’ isused to indicate at the zeolite is physically mixed with salts or oxidesof said metals (or combinations thereof). Mixing will mainly be done bydry mixing, but one may also add some liquid, to improve the mixing. Inthis embodiment, the catalyst of the invention comprises a mixture of azeolite based on rings having 12 oxygen atoms, wherein the zeoliteion-exchanged with palladium and is further loaded with one or moresalts and/or oxides of scandium, yttrium, a lanthanide or a combinationthereof. When salts are used, they will usually be converted intooxides, e.g. during a pretreatment.

The invention further comprises a method for the catalytic reduction ofNO_(x) and a catalyst where the zeolite is loaded with one or moremetals from groups IIIa, IIIb, IVa, IVb, Vb, VIb, VIIb, and VIII of theperiodic system (c), in addition to (a) palladium and (b) scandium,yttrium, a lanthanide or a combination thereof. For example, the zeolitemay be loaded with manganese, vanadium, niobium, gallium, indium,titanium, hafnium or stannum, but the zeolite may also be loaded withgermanium, lead, zirconium, tantalum, chromium, molybdenum, tungstun,rhenium, iron, ruthenium, osmium, cobalt rhodium, iridium, nickel, andplatinum. Here the same applies as described above for scandium,yttrium, etc., viz. that the zeolite may be loaded by ion exchange,incipient wetness techniques or by physically mixing the zeolite withsalts or oxides of said metals (see also below). Also combinations ofthese elements can be used, for example cobalt and platinum, or rhodiumand molybdenum, manganese and cobalt, gallium and platinum, etc., orcombinations of more than two metals from above-mentioned groups can bechosen. The zeolite may be loaded with 0-20% by weight with one or moremetals from groups IIIa, IIIb, IVa, IVb, Vb, VIb, VIIb, and VIII of theperiodic system (c). Here, “% by weight” refers to the amount of zeoliteexchanged with palladium (a) and loaded with oxides or salts (or both)of the metals from Sc, Y or a Ln (b) as well as the metal(s) from GroupVIII of the periodic system (c).

The invention also encompasses in one embodiment a method for thecatalytic reduction of NO_(x) and a catalyst where the zeolite is alsoloaded with 0.01-2% by weight of a second metal from Group VIII of theperiodic system, in addition to palladium. Here, “% by weight” refers tothe amount of zeolite exchanged with palladium (a) and loaded with themetal(s) as oxide(s) or salt(s) of Sc, Y or a Ln (b) and the secondmetal from group VIII of the periodic system (c). Examples of such ametals are cobalt and platinum.

The present invention also encompasses a catalyst as described above.

The process conditions for the catalytic reduction of NO_(x) will dependon the applications. The person skilled in the art will therefore choosethe catalyst volume, the gas speed, the temperature, the pressure andthe quantity of methane (or natural gas), and the composition of thegas, in such a way that the best conversion results are achieved. Goodresults are achieved, for example, at an NO content of about 100 ppm ormore. It is possible to work with an excess of methane. TheNO_(x)/methane ratio is preferably between about 0.02 and 2.

The method can be used at relatively low temperatures. The conversion ofNO_(x) takes place from about 300° C. onwards. Almost completeconversion takes place at about 450° C., At higher temperatures theconversion may decrease somewhat, but good results are still achieved at500° C. The temperature for working is preferably between 300° C. and600° C., more preferably between 350° C. and 450° C.

The method according to the invention can inter alia be used for thecatalytic reduction of NO_(x) which for example is emitted by gasengines, gas burners or emergency power supplies, or NO_(x) which isemitted during caprolactam production, etc.

Thus, gas burners are for example used in horticulture for CO₂fertilization in greenhouses. A trace of NO_(x) can already impede thegrowth of the plants. In generating sets for emergency power supplies,use is usually made of diesel as fuel. In order to remove NO_(x),according to the invention the reducing agent methane can be obtainedfrom the natural gas network. In small-scale combined heat and powerinstallations, gas turbines are also used in addition to gas engines. Inthe case of these turbines, too, NO_(x) has to be removed from theoutlet gases. The technique which makes use of natural gas as thereducing agent (instead of ammonia) is highly suitable for this purpose.

The method according to the invention can also be used in combinationwith a catalyst for the removal of N₂O, so that both NO_(x) and N₂O(laughing gas), which are emitted in the industrial production of nitricacid for example, are removed. A preferred embodiment of this comprisesthe method of the invention in combination with the catalyst for theremoval of N₂O, wherein the latter is an iron-containing zeolite and/ora promoted iron-containing zeolite. In this process a gas containingnitrogen oxide (NO_(x)) and dinitrogen oxide (N₂O) is passed withmethane through a first catalyst, as described above, and the gasobtained is then passed through an additional catalyst, where thisadditional catalyst comprises an iron-containing zeolite and/or apromoted iron-containing zeolite. The term “promoted” means that inaddition to an active element, such as iron, the catalyst contains atleast one additional element which promotes the reaction. Fe-ZSM-5 orFe-MOR, for example, can be chosen as additional catalyst. The term“additional catalyst” refers to any extra catalyst, next to the catalystof the invention. The person skilled in the art may also use acombination of additional catalysts.

NO_(x) and N₂O are also emitted in the production of caprolactam, anylon precursor. The method described above of catalytic reduction of agas containing nitrogen oxides and dinitrogen oxide with methane and thecatalyst combination can also be used here.

The method according to the invention, as described above, can also becombined with other catalysts, e.g., catalysts for the removal ofmethane (such as PdO- or PtO-borne catalysts or example). Such acatalyst can be used to burn any methane left over after the catalyticreduction. The invention therefore also encompasses a method wherein anadditional catalyst is used for the removal of methane, for example thecombination of Ce—Pd-MOR and a PdO- or PtO-borne catalyst, or forexample the combination of Ce—Pd-MOR, Fe-MOR and a PdO- or PtO-bornecatalyst.

The present invention also encompasses a method for the preparation of acatalyst which is suitable for the catalytic reduction of NO_(x) from anNO_(x) containing gas using methane, as described above. In this methodthe zeolite is loaded with scandium, yttrium, a lanthanide or acombination thereof (and optionally other metals) after having beenloaded with palladium by ion exchange (with the aid of a palladium saltin the liquid phase).

As mentioned above, the zeolite is loaded with scandium, yttrium, alanthanide or a combination thereof by ion exchange, incipient wetnesstechniques or by physically mixing the zeolite with salts or oxides ofthese metals. The zeolite may be loaded with 0.01 to 50% by weight ofthese elements (present as oxide, salt or as ion). The person skilled inthe art may choose the appropriate amounts of the metals. Here, “% byweight” refers to the amount of zeolite exchanged with palladium (a) andloaded with the metal(s) as oxide(s) or salt(s) of Sc, Y or a Ln (b).

When physical mixing is used to load the zeolite, the zeolite mayusually be loaded with 0.01 to 50% by weight of scandium, yttrium, alanthanide or a combination thereof. When ion exchange or incipientwetness techniques are used, the zeolite may usually comprise 0.01 to20% by weight of scandium, yttrium, a lanthanide or a combinationthereof. In a further embodiment, the zeolite is e.g. loaded with 0.01to 20% by weight of these elements, more preferably with 1-10% byweight.

In a further embodiment of the method for the preparation of thecatalyst according to the invention, a method may be used, where thezeolite, after having been loaded with palladium by ion exchange, thezeolite is optionally loaded with one or more metals from groups IIIa,IIIb, IVa, IVb, Vb, VIb, VIIb, and VIII of the periodic system, inaddition to (a) palladium and (b) scandium, yttrium, a lanthanide or acombination thereof, before, at the same time or after the introductionof scandium, yttrium or a lanthanide or a combination thereof. Theloading of the catalyst according to the invention with these metals canbe done by ion exchange, incipient wetness techniques or by physicallymixing the zeolite with salts or oxides of said metals. For example whenusing incipient wetness techniques, after the palladium exchange thezeolite can be loaded with 0.01 to 20%, e,g. 0.01-2% by weight of asecond metal from Group VIII of the periodic system, in addition topalladium, before, during or after the introduction of scandium, yttriumand/or lanthanide in the zeolite.

Known salts such as readily soluble nitrates, for example, are used forthe palladium exchange. The H or NH₄ form of the zeolite, such as forexample NH₄-MOR or H-FAU, etc., can for example be used as the zeolite.The exchange is performed long enough (or often enough) for about 0.02to 2% by weight of palladium to be present in the zeolite. The zeoliteis then filtered off, washed and dried. After that the zeolite is loadedwith scandium, yttrium, a lanthanide or a combination thereof. This canbe done by ion exchange or by pore volume impregnation (incipientwetness technique). After that the zeolite is dried and calcined. It canalso be done by a physical mixing (see above).

Hence, the catalyst of the invention comprises a palladium-containingzeolite, wherein the palladium in the zeolite is wholly or partiallycoordinated as ion by the zeolite, wherein the zeolite is based on ringsof 12 oxygen atoms, and wherein the zeolite is also loaded withscandium, yttrium or a lanthanide or a combination thereof, and whereinthe zeolite is optionally also loaded with (c) one or more metals fromgroups IIIa, IIIb, IVa, IVb, Vb, VIb, VIIb, and VIII of the periodicsystem. This catalyst may be prepared and used in various embodiments,as shown in the table below:

optionally one or scandium, yttrium more metals from groups or alanthanide IIIa, IIIb, IVa, IVb, Vb Pd or a combina- VIb, VIIb, and VIIIion tion thereof of the periodic system via ion exchange X X X of thezeolite via incipient — X X wetness techniques via physically — X Xmixing of the zeolite with a salt or oxide

One may also use a combination of methods, e.g. impregnating aPd-exchanged zeolite with scandium, yttrium or a lanthanide or acombination thereof, and then further physically mixing with an oxideone of these metals.

Instead of physically mixing, or next to physically mixing, one may alsouse combinations of catalysts, e.g. a combination of catalysts where thecatalysts are arranged in series. For example, the invention comprisesalso a method and a catalyst where the catalyst comprises a combinationof (cat 1 (a)) a palladium-containing zeolite and (cat 2 (b)) an oxideof scandium, yttrium or a lanthanide or a combination thereof, in whichthe catalysts (cat 1 (a) and cat 2 (b)) are arranged in series. Inanother embodiment the invention comprises a method and a catalyst wherethe catalyst comprises a combination of a palladium-containing zeolitewhich has been loaded with scandium, yttrium or a lanthanide or acombination thereof by incipient wetness techniques (after the ionexchange with palladium) (cat 1(a,b) and an oxide of one or more metalsfrom groups IIIa, IIIb, IVa, IVb, Vb, VIb, VIIb, and VIII of theperiodic system (cat 2 (c)), in which the catalysts (1 (a,b) and 2 (c))are arranged in series.

Here, the phrase “loaded with one or more metals from groups IIIa, IIIb,IVa, IVb, Vb, VIb, VIIb, and VIII of the periodic system, in addition to(a) palladium and (b) scandium, yttrium, a lanthanide or a combinationthereof” describes that the zeolite is exchanged with palladium ions (a)and further loaded scandium, yttrium, a lanthanide or a combinationthereof (b), either by ion-exchange, incipient wetness techniques orphysical mixing with oxides or salts and also loaded with (c) one ormore metals from groups IIIa, IIIb, IVa, IVb, Vb, VIb, VIIb, and VIII ofthe periodic system (either by ion-exchange, incipient wetnesstechniques or physical mixing with oxides or salts). The loading of thezeolite by palladium ions is always the first step. Then the same timeor after each other, the zeolite is loaded with one of the other metals(b,c). Since Pd should be exchanged first, “loaded with one or moremetals from groups IIIa, IIIb, IVa, IVb, Vb, VIb, VIIb, and VIII of theperiodic system in addition to palladium” means “loaded with one or moremetals from groups IIIa, IIIb, IVa, IVb, Vb, VIb, VIIb, and VIII of theperiodic system, with the exception of Pd. However, when a method isused, wherein an additional catalyst is used for the removal of methane,Pd may be comprised as additional catalyst, which will be positioned inseries after the catalyst of the invention (see also above). Thecatalyst of the invention comprises a palladium exchanged zeolite thatis subsequently loaded with scandium, yttrium, a lanthanide or acombination thereof (b), either by ion-exchange, incipient wetnesstechniques or physical mixing (see above). Therefore, the phrase “loadedwith one or more metals from groups IIIb, of the periodic system inaddition to (b) scandium, yttrium, a lanthanide or a combinationthereof” means that the catalyst of the invention comprises a zeolitethat is “loaded with one or more metals chosen from the group consistingof scandium, yttrium, and lanthanides (La and Lu inclusive) (b) and mayoptionally be loaded with one or more metals from group IIIb (belongingto (c)), wherein in the case of a loading with the same loadingtechniques the metals chosen from group (b) and group (c) will usuallybe different, and wherein in the case of a loading with the differentloading techniques the metals chosen from group (b) and group (c) may bethe same or may be different”. Examples of loading with the sametechniques are e.g. ion-exchange for metals chosen from (b) andion-exchange for metals chosen from (c); or a physical mixing for metalschosen from (b) and a physical mixing for metals chosen from (c). Forexample, a zeolite is exchanged with palladium and then impregnated withcerium. The cerium-palladium zeolite may then physically be mixed withcerium oxide.

The invention is also directed to a catalyst that is obtainableaccording to method for the preparation of the catalyst of theinvention.

DESCRIPTION OF THE FIGURES

FIG. 1: CH₄ and NO_(x) conversion over palladium-containing mordenite,wherein the mordenite is loaded with palladium by ion exchange (WIE)(Pd; catalyst 1) or impregnation (IMP) (Pd; catalyst 3).

FIG. 2: FTIR absorption spectra of mordenite which has been impregnatedwith palladium (PdIMP) (Pd; catalyst 3), has been exchanged withpalladium ions (PdWIE) (Pd; catalyst 1) and unloaded mordenite (HMOR).

FIG. 3: NO_(x) conversions over palladium exchanged mordenite (Pd;catalyst 1), cerium loaded mordenite (Ce; catalyst 5), cobalt-palladiumloaded mordenite (Co—Pd; catalyst 4) and cerium-palladium loadedmordenite (Ce—Pd; catalyst 2).

FIG. 4: NO_(x) conversions over cerium-palladium loaded mordenite(catalyst 2) with methane as a function of time at differenttemperatures and gas speeds.

FIG. 5: NO_(x) conversions over cerium-palladium loaded mordenite(catalyst 2) with methane as a function of time at 350° C. and with agas stream that is characteristic of the emissions of a nitric acidfactory.

FIG. 6: Conversions as a function of the temperature of a combineddeNO_(x)/deN₂O setup where the gas is first passed through catalyst 2and then through catalyst 6. Methane is taken as the reducing agent; thegas stream is characteristic of the emissions of a nitric acid factory.FIG. 6 a depicts N₂O conversion at 1 and 6 bara. FIG. 6 b depicts NO_(x)conversion at 1 and 4 bara.

EXAMPLES

Test Apparatus:

The catalytic conversion of NO, NO₂ (and possibly N₂O) with methane wasstudied in a semi-automatic test setup. Gases are supplied withso-called Mass Flow Controllers (MFC) and water is added by means of asaturator which has been set at the right temperature. Pipes are heatedto 130° C. in order to prevent condensation. A quartz reactor with aninternal diameter of 0.6 to 1 cm is placed in an oven for theexperiments. The catalyst sieve fraction (0.5-0.5 mm) is placed on aquartz gauze. Quantitative analysis of the gaseous phase is possibleusing a calibrated Bomen MB100 Fourier transform infra-red (FTIR)spectrometer equipped with a model 9100 gas analyser. The carrier gas(balance) in the examples is N₂.

Example 1 Preparation of Loaded Zeolites

Cat 1: Palladium-MOR (Pd-WIE)

Pd-MOR was prepared by ion exchange. NH₄-MOR powder (Zeolyst, CBV21a)was stirred for 24 h, at 80° C., in a 10% by weight Pd(NO₃)₂ in nitricacid (Aldrich, 10%) solution. After that the zeolite was filtered off,thoroughly washed with demineralized water and dried for 16 h at 80° C.(Pd(WIE)-MOR; here WIE stands for ‘obtained with ion exchange’).

Cat 2: Cerium-Palladium-MOR (Ce-IMP; Pd-WIE)

For the preparation of 4% by wt Ce(IMP)-4% by wt Pd(WIE)-MOR 5 gram of0.4% by weight Pd(WIE)-MOR was then taken and 1 ml of cerium nitrate(Aldrich) was added to it with a density of 1.44 grams per ml. The poreswere precisely filled with this quantity (incipient wetness). Theimpregnated zeolite was then dried for 16 h at 80° C. and after thatcalcined the reactor at 450° C.

Cat 3: Palladium MOR (Pd(IMP))

For the preparation of 0.4% by wt Pd(IMP)-MOR 5 grams of NH₄MOR wastaken and 0.45 grams of 10% Pd(NO₃)₃ in 10% nitric acid was added to it.The impregnated zeolite was then dried for 16 h at 80° C. and after thatcalcined in the reactor at 450° C. (PdIMP means impregnated with Pd).

Cat 4: Cobalt-Palladium MOR (Co(IMP)-Pd(WIE))

For the preparation of 2.3% by wt Co(IMP)-0.4% by wt Pd(WIE)-MOR 5 gramsof Pd(WIE)-MOR was taken and 1 ml of cobalt nitrate (Aldrich) was addedto it with a density of 1.38 grams per ml. The impregnated zeolite wasthen dried for 16 h at 80° C. and after that calcined in the reactor at450° C.

Cat 5: Cerium-MOR (Ce-IMP)

For the preparation of 4% by wt Ce(IMP)-MOR 5 grams of NH₄-MOR was takenand 1 ml of cerium nitrate (Aldrich) was added to it with a density of1.44 grams per ml. The pores were precisely filled with this quantity(incipient wetness). The impregnated zeolite was then dried for 16 h at80° C. and after that calcined in the reactor at 450° C.

Cat 6: Fe-ZSM-5

This catalyst was prepared by the method of preparation described inNL-A-1017245.

Cat 7: Praseodimium-Palladium-MOR (Pr-IMP; Pd-WIE)

For the Pr—Pd combination catalysts, 1 ml of praseodymiumnitrate (9.375gram dissolved in 10 ml demiwater) was added to 5 gram of Pd-MOR (Cat1). In this case the pores of the zeolite were precisely filled(so-called “incipient wetness impregnation”). Finally, the catalyst wasdried for 16 h at 120° C. and calcined at 450° C. in situ.

Cat8: Yttrium-Palladium-MOR (Pr-IMP; Pd-WIE)

For the Y—Pd combination catalysts, 1 ml of yttriumnitrate (11.5 gramdissolved in 10 ml demiwater) was added to 5 gram of Pd-MOR (Cat 1). Inthis case the pores of the zeolite were precisely filled (so-called“incipient wetness impregnation”). Finally, the catalyst was dried for16 h at 120° C. and calcined at 450° C. in situ.

Cat 9: Physical mixture of an a Ln oxide and Cerium-Palladium-MOR(Ce-IMP; Pd-WIE)

As oxide of a lanthanide ceria (CeO₂) was chosen. Cat 8 and ceria werephysical mixed (3:1 w/w).

Cat 10:BEA Ce—Pd

This Catalyst was prepared in the same way as catalyst 2, but now usingBEA as zeolite.

Cat 11:ZSM-5 Ce—Pd

This catalyst was prepared in the same way as catalyst 2, but now usingZSM-5 as zeolite.

Cat 12:FER Ce—Pd

This catalyst was prepared in the same way as catalyst 2, but now usingFER as zeolite.

Example 2 Effect of Preparation

Catalyst 1 and catalyst 3 were measured under the following testconditions, as given in Table 1. The results obtained are given in Table2 and in FIG. 1.

TABLE 1 test conditions for Example 2 Volume 0.9 ml Flow 150 ml/min GHSV10000 h⁻¹ P 1 bara Gas Composition: NO 500 ppm CH₄ 2500 ppm H₂O 5% O₂ 5%N₂ balance

TABLE 2 conversion results from Example 2 (see also FIG. 1) Cat 3 Cat 1T CH₄ conversion NO_(x) conversion CH₄ conversion NO_(x) conversion (°C.) (%) (%) (%) (%) 202 0 0 0 0 222 1 0 0 0 242 1 0 0 0 261 2 0 0 0 2811 0 1 0 302 4 3 1 4 322 4 1 1 9 342 5 6 5 17 362 8 10 5 31 382 12 16 839 402 24 23 10 48 422 43 33 10 61 443 71 38 15 67 463 99 36 29 76 483100 30 58 81 503 100 19 91 83

From these data it is apparent that the Pd-impregnated catalyst (cat 3)burns methane, at the cost of the NO_(x) conversion. Such catalysts aretherefore not suitable for the method of the invention.

FIG. 2 gives FTIR absorptions of mordenite which has been loaded withpalladium by ion exchange or impregnation, and of non-exchangedmordenite. Only in the case of the zeolite exchanged with palladium isan absorption band present at about 950 cm⁻¹, which is characteristic ofPd²⁺ at exchange sites.

Ion exchange with palladium results a shift of the lattice vibrationalband (±1100-1000 cm⁻¹) towards lower wavenumber (between 980 and 920cm⁻¹). As reported by e.g. L. Drozdova, R. Prins, J. Dedecek, Z.Sobalik, B. Wichterlova, J. Phys. Chem. B 106 (200) 2240 and B. Pommier,P. Gelin, Phys. Chem. Chem. Phys. 1 (1999) 1665, this is indicative forpalladium cations co-ordinated at the exchange site positions inside thezeolite micropores. This band is absent in the SCR inactive HMOR samplebefore introduction of palladium and in the SCR inactive catalystprepared by impregnation with palladium (PdIMP).

The interaction of Pd²⁺ in the 12-membered ring channel of zeolite X andY can also be shown by UV-VIS-NIR spectroscopy and ²⁹Si-MAS NMR (Sauvageet al., J. Chem. Soc. Faraday Trans, 1995, 91(18), 3291-3297 and Sauvageet al. Chem. commun. 1996, 1325, respectively). However, also EXAFS maybe used. For instance, Zhang and Sachtler describe in Zeolites Vol. 10,1990 an EXAFS study that indicated the presence of Pd²⁺ in the12-membered ring of zeolite Y.

Example 3 Effect of Promotors

In this example catalyst 2 (cerium-palladium-MOR: Ce-IMP; Pd-WIE),catalyst 3 (palladium-MOR: Pd-WIE), catalyst 4 (cobalt-palladium-MOR:Co-IMP; Pd-WIE) and catalyst 6 (cerium-MOR: Ce-IMP) a compared. The testconditions are as shown in Table 3, the results are given in Table 4 andin FIG. 3.

TABLE 3 test conditions for Example 3 Volume 0.45 ml Flow 150 ml/minGHSV 20000 h⁻¹ P 1 bara Gas composition: NO 500 ppm CH₄ 2500 ppm H₂O 5%O₂ 5% N₂ balance

TABLE 4 conversion results from Example 3 (see also FIG. 3) NO_(x)conversion (%) Cat. 3 Cat. 6 Cat. 4 Cat. 2 T (° C.) Pd Ce Co—Pd Ce—Pd200 0 0 0 0 220 0 0 0 0 240 0 0 0 0 260 0 0 0 0 280 0 0 1 1 300 1 0 4 1320 2 0 6 6 340 4 0 19 15 360 7 0 29 28 380 10 0 44 42 400 13 0 52 55420 19 0 56 71 440 28 0 61 82 450 38 0 63 470 0 490 0

From the data it is apparent that both cerium and cobalt increase theactivity of Pd-MOR. Above about 400° C. the conversion of the Ce—Pd-MORcatalyst is better. Ce-MOR does not show any activity at all, however,for the conversion of NO to N₂ with methane.

Example 4 Stability of Ce—Pd-MOR for Exhaust Gases from InternalCombustion Engines

In this example the stability of catalyst 2 is measured at different gasspeeds and at different temperatures. The test conditions are given inTable 5, and the results of measurement are given in Table 6 (alsocomparison with catalyst 4 Co(IMP)-Pd(WIE)-MOR) and are reproduced inFIG. 4. The gas composition is characteristic of the composition of theexhaust gases from an internal combustion engine.

TABLE 5 test conditions for Example 4 Volume 0.45-1.8 ml Flow 150 ml/minGHSV 5000-20000 h⁻¹ P 1 bara Gas composition: NO 500 ppm CH₄ 2500 ppmH₂O 5% O₂ 5% N₂ balance

From the results below (Table 6, FIG. 4) it is apparent that in spite ofthe presence of 5% water (and 5% oxygen) the catalyst retains itsactivity at both temperatures. It is also apparent from the comparisonof cat 2 (Ce(IMP)-Pd(WIE)-MOR) and cat 4 (Co(IMP)-Pd(WIE)-MOR) in Table6 that the stability of cat 2 is higher.

TABLE 6 conversion results from Example 4 (see also FIG. 4 forCe—Pd-MOR) Ce(IMP)—Pd Ce(IMP)—Pd Ce(IMP)—Pd (WIE)-MOR (WIE)-MOR(WIE)-MOR Time T 370° C.; T 420° C.; T 420° C.; (h) 5000 h⁻¹ 20000 h⁻¹20000 h⁻¹ 2 61 63 56 5 59 63 58 10 60 63 60 15 58 61 56 20 58 63 56 2559 64 54 30 57 63 53 35 60 61 53 40 57 62 51 45 57 62 47 50 59 63 44 5557 60 58 65 57 70 58 75 57 80 59

Example 5 Stability of Ce—Pd-MOR for Nitric Acid Exhaust Gas Conditions

In this example catalyst 2 is used to remove NO_(x) from a gascomposition such as to be found in the outlet gases from a nitric acidfactory. The conditions are given in Table 7 and the results in Table 8and in FIG. 5.

TABLE 7 test conditions for Example 5 Volume 15 ml Flow 5 l/min GHSV20000 h⁻¹ P 4 bara Gas composition: N₂O 1500 ppm NO 500 ppm CH₄ 2500 ppmH₂O 0.5% O₂ 2.5% N₂ balance

TABLE 7 conversion results from Example 5 at 350° C. (see also FIG. 5)Time (h) NO_(x) (%) Time (h) NO_(x) (%) Time (h) NO_(x) (%) 0 67 34 6268 63 2 66 36 62 70 62 4 65 38 62 72 62 6 66 40 62 74 61 8 65 42 62 7662 10 64 44 62 78 61 12 63 46 62 80 62 14 63 48 62 82 62 16 62 50 62 8462 18 63 52 61 86 62 20 62 54 62 88 61 22 62 56 62 90 61 24 62 58 63 9262 26 63 60 62 94 61 28 63 62 63 96 61 30 62 64 62 98 61 32 62 66 62

From these results (Table 8, FIG. 5) it is apparent that the catalystretains its activity for a long time at 350° C. in the presence of 0.5%water (and 2.5% oxygen) and 1500 ppm N₂O.

Example 6 Combined NO_(x)-N₂O Removal

In this example a combined deNO_(x)-deN₂O setup is used, as described inNL-A-1017245, and in which the first catalyst is now catalyst 2 and thesecond catalyst is catalyst 6. Methane is used as reduction gas. Thereaction conditions are given in Table 8, and are as in outlet gasesfrom a nitric acid factory. The test results are shown in Table 9 andare also given in FIG. 6. From the results it is apparent that goodNO_(x) and N₂O conversions can be achieved at relatively lowtemperatures. Even better conversions are achieved at pressures higherthan 1 bara (FIG. 6 a: N₂O conversion at 1 and 6 bara; FIG. 6 b: NO_(x)conversion at 1 and 4 bara).

TABLE 8 test conditions for Example 6 Cat 2 Cat 6 Volume 15 ml 15 mlFlow 5 l/min GHSV 20000 h⁻¹ P 1 and 4 bara Gas composition: N₂O 1500 ppmNO  500 ppm CH₄ 2500 ppm H₂O 0.5% O₂ 2.5% N₂ balance

TABLE 9 NO_(x) and N₂O conversion results from Example 6 (see also FIG.6a & 6b) 1 bara 4 bara T (° C.) N₂O (%) NO_(x) (%) N₂O (%) NO_(x) (%)263 0 5 0 19 290 1 7 1 20 318 7 12 10 28 346 26 24 47 57 375 61 41 98 94405 95 63 100 100 436 100 82 98 100 466 100 88 100 99

Example 7 Conversion of NO_(x) and CH4 and Stability of Y—Pd-MOR

Catalyst 8 was measured for evaluation of the conversion and stability,under the test conditions as given in Tables 10 and 12, respectively.The results obtained are given in tables 11 and 13, respectively.

TABLE 10 test conditions for Example 7 (conversion) Example CH₄-SCR:performance yttrium—Pd-MOR Volume 0.45 ml Flow 100 ml/min GHSV 13500 h⁻¹P 1 bara Gas composition NO 500 ppm CH₄ 2500 ppm H₂O 5% O₂ 5% N₂ bal.

TABLE 11 conversion results for Pr—Pd-MOR (Cat 8) Yttrium—Pd-MOR T (°C.) CH₄ % NO_(x) % 260 0 0 281 0 0 302 0 0 322 0 0 342 1 3 362 2 5 382 313 392 3 18 412 4 27 433 9 50 453 22 85 473 55 98 490 89 100

TABLE 12 test conditions for Example 7 (stability) Example CH₄-SCR:performance yttrium—Pd-MOR Volume 0.9 ml Flow 100 ml/min GHSV 7000 h⁻¹ T395 ° C. P 1 bara Gas composition NO 500 ppm CH₄ 2500 ppm H₂O 10.5% O₂  5% N₂ bal.

TABLE 13 Performance for Y—Pd-MOR (Cat 8): conversion at 400° C. as afunction of time T 400° C.; 7.000 h⁻¹ Conversion (%) Time (h) CH₄ NO_(x) 2 10 58 100  9 53 150 10 54 200 10 55 250  9 54 300 11 56 350  9 54 40010 55 450 11 52

Yttrium (yttria) improves the SCR activity of palladium-MOR resulting tohigher NO_(x) conversion level as compared to palladium. Yttrium(yttria) stabilizes Pd-MOR, even in the presence of over 10% water inthe feed.

Example 8 Stability of Pr—Pd-MOR

Catalyst 7 was measured for evaluation of the stability, under the testconditions as given in Table 14. The results obtained are given in Table15.

TABLE 14 test conditions for Example 8 (Stability) Example CH₄-SCR:Stability Praseodymium—Pd-MOR Volume 0.7 ml Flow 100 ml/min GHSV 9.000h⁻¹ T 420 deg C. P 1 bara Gas composition NO 500 ppm Ch₄ 2500 ppm H₂O 5%O₂ 5% N₂ bal.

TABLE 15 Performance for Pr—Pd-MOR (Cat 7): conversion at 420° C. as afunction of time T 420° C.; 9.000 h⁻¹ Conversion (%) Time (h) CH₄ NO_(x) 2 11 59 10 14 60 23 14 63 80 14 65 85 15 64

Praseodymium improves the SCR activity of palladium-MOR resulting in ahigher NO_(x) conversion level as compared to palladium alone.Praseodymium stabilizes Pd-MOR and shows no signs of deactivation forthe period of the test (85 hour).

Example 9 Conversion of NO_(x) and CH₄ on a Number of PalladiumExchanged Mordenities

A number of palladium exchanged mordenites were measured for evaluationof the conversion, under the test conditions as given in Table 16. Theresults obtained are given in Table 17. The lanthanum (La), dysprosium(Dy) and gadolinium (Gd) Pd-mordenites were prepared in the same way asdescribed for Cat 7 and 8.

TABLE 16 test conditions for Example 9 (conversion) Example CH₄-SCR:performance Lanthanides-Pd-MOR Volume 0.45 ml Flow 100 ml/min GHSV 13500h⁻¹ P 1 bara Gas composition NO 500 ppm CH₄ 2500 ppm H₂O 5% O₂ 5% N₂bal.

TABLE 17 conversion of NO_(x) and CH₄ on Pd-exchanged mordenites Pr—Pd-Tb—Pd- La—Pd- Dy—Pd- Gd—Pd- Pd-MOR MOR MOR MOR MOR MOR T CH₄ NO_(x) CH₄NO_(x) CH₄ NO_(x) CH₄ NO_(x) CH₄ NO_(x) CH₄ NO_(x) (° C.) % % % % % % %% % % % % 259 0 0 0 0 nd nd 0 0 0 0 0 0 269 0 0 0 0 nd nd 0 0 0 0 0 0279 0 0 0 0 nd nd 0 0 0 0 0 0 288 0 0 0 0 nd nd 0 0 0 0 0 0 298 0 0 0 00 0 0 0 0 0 0 0 308 0 0 0 0 0 0 0 0 0 0 0 0 318 0 0 0 0 0 0 1 0 0 0 0 0328 0 0 0 0 0 0 1 4 1 1 2 4 338 2 7 2 9 0 0 2 9 2 5 3 3 348 1 8 2 11 0 03 9 2 2 3 5 357 3 8 3 10 0 4 3 11 2 6 5 6 367 8 11 4 11 1 5 3 13 2 9 4 8377 5 13 4 12 1 8 3 15 3 11 4 11 387 5 15 3 14 4 8 3 18 2 10 3 13 397 417 6 15 5 14 4 21 4 16 4 14 406 5 21 7 22 5 15 5 25 4 21 6 17 416 7 2310 24 4 17 7 29 7 26 4 17 426 9 25 8 27 5 20 8 37 7 35 8 22 436 17 30 1138 7 24 12 48 10 50 10 29 445 21 41 14 66 11 37 18 57 16 67 16 48 455 2954 27 82 15 53 27 71 24 87 22 75 464 45 70 42 100 24 81 42 80 39 94 3690 474 72 79 59 100 35 99 68 86 59 97 54 99 483 94 79 77 100 53 100 9489 78 97 72 97 493 90 100 72 100 100 86 93 99 93 100

Lanthanides improve the SCR activity of palladium-MOR resulting inhigher NO_(x) conversion levels as compared to palladium mordenite (ionexchanged) only.

Example 10 Conversion of NO_(x) and CH₄ on a Physical Mixture of aZeolite and an Oxide (Cat 9)

Cat 9 was measured for evaluation of the conversion, under the same testconditions as given in Table 16. The result obtained are given in Table18.

TABLE 18 conversion results for Cat 9 CeO₂ + Yttrium—Pd-MOR T (° C.) CH₄% NO_(x) % 260 0 0 281 0 0 302 0 0 318 5 19 338 8 45 362 15 72 377 20 88387 22 92 407 26 94 427 33 99 456 50 99 475 67 99 495 91 99

Physical mixing of ceria and Y—Pd-CBV21a (1:3 w/w) gives a very high SCRactivity.

Example 11 Conversion of NO_(x) and CH₄ on BEA (Cat 10) Compared toZSM-5 (Cat 11)

Ce—Pd-BEA (Ce IMP, Pd WIE) Cat 10 was measured for evaluation of theconversion in comparison to Ce—Pd-ZSM-5 (Ce IMP; Pd WIE) (Cat 11), underthe same test conditions as given in Table 3. The results obtained aregiven in Table 19.

TABLE 19 conversion results for Ce—Pd-BEA (Ce IMP; Pd WIE) Cat 10 andCe—Pd-ZSM-5 (Ce IMP; Pd WIE) (Cat 11) cerium—Pd-ZSM-5 cerium—Pd-BEA(10-ring) (12-ring) T (° C.) CH₄ % NO_(x) % CH₄ % NO_(x) % 276 0 0 0 0295 0 0 0 0 315 0 0 0 0 334 1 6 1 8 353 3 9 4 14 372 4 15 5 17 391 5 227 24 410 10 26 12 30 430 15 32 18 35 450 22 33 24 49

Compared to Ce(IMP)-Pd(WIE)-ZSM-5 (10-ring zeolite), theCe(IMP)-Pd(WIE)-BEA catalyst (12-ring zeolite) is more active for NO_(x)SCR with methane.

Example 12 Conversion of NO_(x) and CH₄ on Ce—Pd-ZSM-5 and Stability ofCe—Pd-ZSM-5 (Not According to the Invention)

Ce—Pd-ZSM-5 (Ce IMP; Pd WIE) Cat 11 was measured for evaluation ofconversion and performance (stability), under the test conditions asgiven in Table 3 (with 19500 instead of 20000 h⁻¹) and table 21,respectively. The result obtained are given in Tables 20 and 22,respectively.

TABLE 20 conversion results for Ce—Pd-ZSM-5 (Ce IMP; Pd WIE) Cat 11cerium—Pd-ZSM-5 T (° C.) CH₄ % NO_(x) % 199 0 0 219 0 0 238 0 0 257 0 0276 0 0 295 0 0 315 0 0 334 1 6 353 3 9 372 4 15 391 5 22 410 10 26 43016 32 450 22 33

TABLE 21 test conditions for Ce—Pd-ZSM-5 (Ce IMP; Pd WIE) Cat 11(Stability) Example CH₄-SCR: stability of Ce—Pd-ZSM-5 as a function ofthe temperature Volume 0.45 ml Flow 150 ml/min GHSV 19.500 h⁻¹ T 450 °C. P 1 bara

TABLE 22 test results for Ce—Pd-ZSM-5 (Ce IMP; Pd WIE) Cat 11(Stability) Time (h) CH₄(%) NO_(x) (%) 2 18 23 5 14 18 10 13 16 15 12 1220 11 12 25 11 12 30 10 11 35 9 11 40 8 9 45 7 8 50 7 7

It appears that the Ce(IMP)-Pd(WIE)-ZSM5 catalyst is not very activecompared to Ce—Pd-MOR and even deactivates with time.

Example 13 Conversion of Ce—Pd-FER (Not According to The Invention)

Ce—Pd-FER (Ce IMP; Pd WIE) Cat 12 was measured for evaluation of theconversion and performance (stability), under the test conditions asgiven in Table 10. The results obtained are given in Table 23.

TABLE 23 conversion of NO_(x) and CH₄ on Ce—Pd-FER (Ce IMP; Pd WIE) Cat12 cerium—Pd-FER (10/8 ring) T (° C.) CH₄ % NO₂ % NO_(x) % 200 0 0 0 2190 0 0 238 0 0 0 258 0 3 0 277 0 4 0 297 0 7 0 316 1 10 0 335 2 12 0 3552 14 0 374 2 22 0 393 2 19 0 412 3 27 0 431 6 23 0

The Ce(IMP)-Pd(WIE)-FER catalyst is only active for the oxidation of NOto NO₂. However, NO_(x) (including NO₂ that has been obtained after theconversion by this catalyst), is not reduced at all.

1. A method for the catalytic reduction of NO_(x) in an NO_(x)containing gas by contacting said NO_(x) containing gas with methane inthe presence of a catalyst comprising a zeolite loaded with palladiumand a metal selected from the group consisting of scandium, yttrium, alanthanide and a combination thereof, said zeolite based on rings having12 oxygen atoms, and wherein said zeolite is loaded with 0.02 to 2% byweight of palladium.
 2. The method according to claim 1, wherein thezeolite is loaded with scandium, yttrium, a lanthanide or a combinationthereof and optionally other metals after having been loaded withpalladium by ion exchange.
 3. The method according to claim 1, whereinthe zeolite comprises a zeolite of the class of FAU, MOR, BEA, EMT, CON,BOG or ITQ-7.
 4. The method according to claim 1, wherein the zeolite isloaded with scandium, yttrium, a lanthanide or a combination thereof byion exchange or incipient wetness techniques.
 5. The method according toclaim 4, wherein the zeolite comprises 0.01 to 20% by weight ofscandium, yttrium, a lanthanide or a combination thereof.
 6. The methodaccording to claim 1, wherein the zeolite comprises 0.01 to 20% byweight of scandium, yttrium, a lanthanide or a combination thereof. 7.The method according to claim 1, wherein the zeolite is further loadedwith one or more metals from groups IIIa, IIIb, IVa, IVb, Vb, VIb, VIIb,and VIII of the periodic system.
 8. The method according to claim 1,wherein the gas comprises oxygen, water or a combination thereof.
 9. Themethod according to claim 1, wherein the gas comprises carbon monoxide.10. The method according to claim 1, wherein the reaction temperature isbetween 30° C. and 600° C.
 11. The method according to claim 1, whereinthe NO_(x)/methane ratio is between 0.02 and
 2. 12. A method for thecatalytic reduction of NO_(x) in an NO_(x) containing gas by contactingsaid NO_(x) containing gas with methane in the presence of a catalystcomprising a zeolite loaded with palladium and a metal selected from thegroup consisting of scandium, yttrium, a lanthanide and a combinationthereof, said zeolite based on rings having 12 oxygen atoms, and whereinan additional catalyst is used for the removal of N₂O.
 13. The methodaccording to claim 12, wherein the additional catalyst for the removalof N₂O is an iron-containing zeolite, a promoted iron-containing zeoliteor a combination thereof.
 14. A method for the catalytic reduction ofNO_(x) in an NO_(x) containing gas by contacting said NO_(x) containinggas with methane in the presence of a catalyst comprising a zeoliteloaded with palladium and a metal selected from the group consisting ofscandium, yttrium, a lanthanide and a combination thereof, said zeolitebased on rings having 12 oxygen atoms, and wherein an additionalcatalyst is used for the removal of methane.
 15. A method for thecatalytic reduction of NO_(x) in an NO_(x) containing gas by contactingsaid NO_(x) containing gas with methane in the presence of a catalystcomprising a zeolite loaded with palladium and a metal selected from thegroup consisting of scandium, yttrium, a lanthanide and a combinationthereof, said zeolite based on rings having 12 oxygen atoms, wherein thezeolite is loaded with scandium, yttrium, a lanthanide or a combinationthereof by physically mixing the zeolite with salts or oxides of saidmetals, and further wherein an additional catalyst is used for theremoval of N₂O.
 16. The method according to claim 15, wherein thezeolite is loaded with 0.01 to 50% by weight of scandium, yttrium, alanthanide or a combination thereof.
 17. The method according to claim15, wherein the zeolite is further loaded with one or more metals fromgroups IIIa, IIIb, IVa, IVb, Vb, VIb, VIIb, and VIII of the periodicsystem.
 18. The method according to claim 15, wherein the gas comprisesoxygen, water or a combination thereof.
 19. The method according toclaim 15, wherein the gas comprises carbon monoxide.
 20. The methodaccording to claim 15, wherein the reaction temperature is between 300°C. and 600° C.
 21. The method according to claim 15, wherein theNO_(x)/methane ratio is between 0.02 and
 2. 22. The method according toclaim 15, wherein the additional catalyst for the removal of N₂O is aniron-containing zeolite, a promoted iron-containing zeolite or acombination thereof.
 23. A method for the catalytic reduction of NO_(x)in an NO_(x) containing gas by contacting said NO_(x) containing gaswith methane in the presence of a catalyst comprising a zeolite loadedwith palladium and a metal selected from the group consisting ofscandium, yttrium, a lanthanide and a combination thereof, said zeolitebased on rings having 12 oxygen atoms, wherein the zeolite is loadedwith scandium, yttrium, a lanthanide or a combination thereof byphysically mixing the zeolite with salts or oxides of said metals, andfurther wherein an additional catalyst is used for the removal ofmethane.
 24. A catalyst comprising a zeolite loaded with palladium and ametal selected from the group consisting of scandium, yttrium, alanthanide and a combination thereof, said zeolite based on rings having12 oxygen atoms, wherein the palladium in the zeolite is wholly orpartially coordinated as ion by the zeolite, and wherein said zeolite isloaded with 0.02 to 2% by weight of palladium.
 25. The catalystaccording to claim 24, having an infra-red sensitive zeolite latticevibration visible at about 950 cm⁻¹.
 26. The catalyst according to claim24, wherein the zeolite comprises a zeolite of the class of FAU, MOR,BEA, EMT, CON, BOG or ITQ-7.
 27. The catalyst according to claim 24,wherein the zeolite comprises 0.01 to 20% by weight of scandium,yttrium, a lanthanide or a combination thereof.
 28. The catalystaccording to claim 24, wherein the zeolite is further loaded with one ormore metals from groups IIIa, IIIb, IVa, IVb, Vb, VIb, VIIb, and VIII ofthe periodic system.
 29. A method for the preparation of a zeoliteloaded with palladium and a metal selected from the group consisting ofscandium, yttrium, a lanthanide and a combination thereof, said zeolitebased on rings having 12 oxygen atoms, wherein the zeolite is loadedwith scandium, yttrium, a lanthanide or a combination thereof andoptionally other metals after having been loaded with palladium by ionexchange.
 30. The method according to claim 29, wherein the zeolitecomprises a zeolite of the class of FAU, MOR, BEA, EMT, CON, BOG orITQ-7.
 31. The method according to claim 29, wherein the zeolite isloaded with 0.02 to 2% by weight of palladium.
 32. The method accordingto claim 29, wherein the zeolite is loaded with scandium, yttrium, alanthanide or a combination thereof by ion exchange or incipient wetnesstechniques.
 33. The method according to claim 32, wherein the zeolitecomprises 0.01 to 20% by weight of scandium, yttrium, a lanthanide or acombination thereof.
 34. The method according to claim 29, wherein thezeolite comprises 0.01 to 20% by weight of scandium, yttrium, alanthanide or a combination thereof.
 35. The method according to claim29, wherein the zeolite, after having been loaded with palladium by ionexchange, the zeolite is loaded with one or more metals from groupsIIIa, IIIb, IVa, IVb, Vb, VIb, VIIb, and VIII of the periodic system,before, at the same time or after the introduction of scandium, yttriumor a lanthanide or a combination thereof.
 36. The method according toclaim 29, wherein the metal is yttrium.
 37. A method for the catalyticreduction of NO_(x) in an NO_(x) containing gas by contacting saidNO_(x) containing gas with methane in the presence of a catalystcomprising a zeolite loaded with palladium and yttrium, wherein saidzeolite is based on rings having 12 oxygen atoms.
 38. A method for thecatalytic reduction of NO_(x) in an NO_(x) containing gas by contactingsaid NO_(x) containing gas with methane in the presence of a catalystcomprising a zeolite loaded with palladium and yttrium, wherein saidzeolite based on rings having 12 oxygen atoms, and said zeolite isloaded with yttrium by physically mixing the zeolite with salts oroxides of yttrium.
 39. A catalyst comprising a zeolite loaded withpalladium and yttrium, said zeolite based on rings having 12 oxygenatoms, wherein the palladium in the zeolite is wholly or partiallycoordinated as ion by the zeolite.